Intra-Event Trends in Stable Isotopes Exploring Midlatitude Precipitation Using a Vertically Pointing Micro Rain Radar

• Published in: Journal of hydrometeorology Vol. 16; no. 1; pp. 194 - 213
• Main Authors: Muller, Catherine L., Baker, Andy, Fairchild, Ian J., Kidd, Chris, Boomer, Ian
• Format: Journal Article
• Language: English
• Published: Boston American Meteorological Society 01.02.2015
• Subjects: Air masses; Annual rainfall; Atmosphere; Atmospheric precipitations; Chemical composition; Clouds; Composition; Deuterium; Drop size; Environmental science; Evaporation; Geography; Hydrogen; Hydrogen isotopes; Ice; Isotope composition; Isotopes; Land surface models; Measurement techniques; Melting; Monthly rainfall; Precipitation; Precipitation processes; Process parameters; Radar; Rain; Rain intensity; Rain water; Raindrop velocity; Raindrops; Stable isotopes; Synoptic conditions; Trends; Unmanned aerial vehicles; Vapors; United Kingdom > UK
• ISSN: 1525-755X; 1525-7541
• DOI: 10.1175/jhm-d-14-0038.1

Annual, monthly, and daily analyses of stable isotopes in precipitation are commonly made worldwide, yet only a few studies have explored the variations occurring on short time scales within individual precipitation events, particularly at midlatitude locations. This study examines hydrogen isotope data from sequential, intra-event samples from 16 precipitation events during different seasons and a range of synoptic conditions over an 18-month period in Birmingham, United Kingdom. Precipitation events were observed simultaneously using a vertically pointing micro rain radar (MRR), which, for the first time at a midlatitude location, allowed high-resolution examination of the microphysical characteristics (e.g., rain rate, fall velocity, and drop size distributions) that may influence the local isotopic composition of rainwater. The range in the hydrogen isotope ratio (δD, where D refers to deuterium) in 242 samples during 16 events was from −87.0‰ to +9.2‰, while the largest variation observed in a single event was 55.4‰. In contrast to previous work, the results indicate that some midlatitude precipitation events do indeed show significant intra-event trends that are strongly influenced by precipitation processes and parameters such as rain rate, melting-level height, and droplet sizes. Inverse relationships between rain rate and isotopic composition are observed, representing an example of a local type of “amount effect,” a still poorly understood process occurring at different scales. For these particular events, the meanδvalue may therefore not provide all the relevant information. This work has significance for the testing and development of isotope-enabled cloud-resolving models and land surface models at higher resolutions, and it provides improved insights into a range of environmental processes that are influenced by subsampled precipitation events.